Vietnam today formally rejected a U.N. General Assembly resolution calling for an international conference aimed at securing withdrawal of Hanoi's forces from Cambodia and U.N.-supervised elections to establish a new government.

A commentary broadcast by Radio Hanoi said, "Such a conference will yield no results and all resolutions adopted by it will be of no value."

Calling the resolution "an arrogant challenge," Hanoi noted that it was debated and passed without participation of the Heng Samrin administration, "the only legal and authentic government" of Cambodia, the broadcast said.

Hanoi's army installed Heng Samrin in Phnom Penh in January 1979. The United Nations, however, has refused to recognize his government. Earlier this month, the General Assembly voted for the second year in a row to keep the ousted Khmer Rouge government of Pol Pot in Cambodia's seat.

The proposed conference would convence early next year. The resolution creating it was spearheaded by the five Western-oriented members of the Association of Southeast Asian Nations, which continues to recognize the Khmer Rouge. It was supported by China and the United States.

Radio Hanoi called the vote a plot to "trample upon Kampuchean [Cambodian] independance, sovereignty and territorial integrity." Vietnamese forces are in Cambodia at the invitation of Phnom Penh, Hanoi has said, to protect the country against China and the Khmer Rouge.

The commentary asked: "Do the United States, China and their followers accept United Nations participation in elections in their countries?"

Yesterday's assembly resolution said the conference should be attended by all parties to the Cambodian conflict. However, U.N. representatives of Vietnam, Laos and Soviet Bloc countries were reported to have disclosed even before the vote that their countries would not attend.